1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display device and a method of fabricating the same.
2. Description of the Related Art
In general, an organic light emitting diode (OLED) includes an organic layer interposed between a first electrode (i.e., an anode) and a second electrode (i.e., a cathode). The first electrode is a transparent electrode formed of, for example, indium tin oxide (ITO), and the second electrode is formed of a metal having a low work function, such as Ca, Li, or Al. When a forward voltage is applied to the OLED, holes emitted from the anode combine with electrons emitted from the cathode to form excitons, and while the excitons are making the transition from an excited state to a ground state, light is emitted.
The first electrode is generally formed as a reflective electrode that reflects light, while the second electrode is generally formed as a transmissive electrode that transmits light. Thus, the OLED may be fabricated so that light is emitted by the organic layer toward the second electrode.
In this case, the organic layer may be formed by various methods. For example, the organic layer may be formed by a deposition method. Specifically, the deposition of the organic layer includes closely adhering a mask having the same pattern as a thin layer to be formed on an underlying layer, and depositing the thin layer.
FIG. 1 is a cross-sectional schematic view of a deposition apparatus having a deposition mask.
Referring to FIG. 1, in a method of depositing a thin layer of an OLED display device (i.e., an organic layer having an emission layer (EML)), a frame 4 including a mask 1 is positioned at a portion corresponding to a crucible 3 installed in a vacuum chamber 2, and a target 5 (e.g., a pixel defining layer) on which a thin layer will be formed is mounted on the frame 4. A magnet unit 6 is driven to closely adhere the mask 1 and frame 4 to the target 5 on which the thin layer will be formed. A material contained in the crucible 3 is then deposited on the target 5.
However, the surface of the mask 1 may include inconsistencies (or unevenness) of about 2 to 3 μm. Thus, when the mask 1 is too closely adhered to the target 5, the target 5 may be scratched from the inconsistencies in the mask 1. Accordingly, a spacer structure is typically formed between the target 5 and the mask 1 in order to prevent damage to the pixel defining layer.
FIGS. 2A and 2B are cross-sectional schematic views illustrating a method of fabricating a conventional OLED display device.
Referring to FIG. 2A, a buffer layer 110 is formed on a substrate 100. A semiconductor layer including source and drain regions 120a and 120b and a channel region 121 is formed on the buffer layer 110. A gate insulating layer 130 is formed on the semiconductor layer, and a gate electrode 131 is formed on the gate insulating layer 130. An interlayer insulating layer 140 is formed on the gate insulating layer 130, and source and drain electrodes 150a and 150b are formed on the interlayer insulating layer 140 and electrically connected to the source and drain regions 120a and 120b, respectively, through contact holes.
An OLED is then formed. The OLED includes a first electrode 180 and a pixel defining layer 190. The first electrode 180 is formed on a protective layer 160 and a planarization layer 170, which are, in turn, formed on a thin film transistor (TFT). The first electrode 180 functions as an anode that is electrically connected to the drain electrode 150b through a via hole. The pixel defining layer 190 exposes a region of the first electrode 180, and has an opening defining a pixel.
A spacer film is coated on the pixel defining layer 190, and a photoresist layer is formed on the spacer film, and exposed and developed using a shadow mask, thereby forming a photoresist pattern. Thereafter, the spacer film is patterned using the photoresist pattern as a mask, forming a spacer pattern 191.
Referring to FIG. 2B, an organic layer 192 having an EML is formed using the deposition apparatus having the deposition mask, described above with reference to FIG. 1. A second electrode 193 is formed on the organic layer 192 using a sputtering process. In this case, when the organic layer 192 is formed using the deposition apparatus, the spacer pattern prevents or protects the pixel defining layer 190 from being damaged from inconsistencies in the deposition mask.
However, in this conventional method of fabricating the OLED display device, an extra photolithography process for forming the spacer pattern is added, and additional material costs for the spacer film are incurred.
Furthermore, since the spacer pattern is formed by patterning the spacer film using the photolithography process, a residual layer of the spacer film may remain on the first electrode.